The present invention relates to the use of magnesium-copper compositions for the evaporation of magnesium and to magnesium dispensers employing these compositions. Magnesium has recently found a new field of application in the production of OLED displays (Organic Light Emission Displays) and in the so-called “Top Emission OLEDs”, which are referred to in the field as TOLEDs.
In summary, an OLED display is made of a double-layer or of a multi-layer of different organic materials, positioned between two series of electrodes being perpendicular to one another, one series being formed of cathodes and one series being formed of anodes. This assembly is accommodated in a hermetically closed container, which is provided with at least one transparent face that is the area where the image is displayed. For a detailed description of the structure and of the operation of OLED displays, reference may be made, for example, to U.S. Pat. No. 6,013,384. For the TOLED configuration, reference may be made to U.S. Pat. No. 6,770,502.
In the OLEDs, magnesium is used in alloy with silver in order to produce the cathodes, arranged as disclosed in U.S. Pat. No. 6,255,774 (although the latter refers to cathodes made from alkaline metals, lithium in particular) or in the article “Transparent stacked organic light emitting devices. I. Design principles and transparent compound electrodes” by G. Gu et al., J. Appl. Phys. 86, (8) 4067 (1999).
The production of deposits containing magnesium is carried out by evaporation of the magnesium and condensation thereof on the required portions of the OLED (in particular, in the cited patent co-evaporation of magnesium and silver is carried out).
Magnesium evaporation may be carried out from pure metal sources, but this exhibits some drawbacks. In fact, metallic magnesium is rather reactive towards atmospheric gases and humidity. Possible compounds formed upon exposure of magnesium to air, such as the oxide, the hydroxide or the carbonate, make the evaporation of the element less reproducible and would result in pollution of the formed deposits by oxygen and carbon. Consequently, the use of pure magnesium requires a constant treatment in a controlled atmosphere, which makes complex the operations of transporting and stocking, which are preliminary to the use of pure magnesium. Therefore, it is preferable to use magnesium not in the form of pure metal, but in the form of compositions which are stable in air at room temperature.
Japanese Patent No. JP-47-044415 discloses a system for evaporating magnesium, based on the use of magnesium and aluminum alloys, and particularly on compositions containing beta and gamma phases in the Al—Mg phase diagram. However, magnesium evaporation from these alloys is very sensitive to temperature variations and its rate is thus poorly controllable, in particular during the initial steps. In addition, chemical analyses carried out on evaporated films starting from these alloys have determined the presence of aluminum, although in small amounts, which is undesirable since it can modify the electrical characteristics of the cathodes.
International patent application publication WO 2005/111260 discloses a method for evaporating metals chosen among alkaline, alkaline-earth and lanthanide metals. The method includes in forming a compound of these metals which is stable at room temperature, introducing powders of this compound into a filiform metal container (e.g., made of steel) provided with openings for the evaporation of the alkaline, alkaline-earth or lanthanide metal, and heating the filiform system by direct flow of electric current through the metal of the container. Compounds useful to provide magnesium evaporation cited in WO 2005/111260 are magnesium-aluminum, magnesium-indium and magnesium-silver alloys.